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- Author or Editor: E. Y. Hsu x
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Abstract
Studies have shown the advantages of low-frequency (<5 GHz) microwave sensors for soil moisture estimation. Although higher frequencies have limited soil moisture retrieval capabilities, there is a vast quantity of systematic global high-frequency microwave data that have been collected for 15 yr by the Special Sensor Microwave Imager (SSM/I). SSM/I soil moisture studies have mostly utilized antecedent precipitation indices as validation, while only a few have employed limited ground observations, which were typically not optimal for this particular type of satellite data. In the Southern Great Plains (SGP) hydrology experiments conducted in 1997 and 1999, ground observations of soil moisture were made over an extended region for developing and validating large-scale mapping techniques. Previous studies have indicated the limitations of both the higher-frequency data and models for soil moisture retrieval. Given these limitations, an alternative retrieval technique that utilizes multipolarization observations was implemented and tested for the SGP region. A technique for extracting algorithm parameters from the observations was developed and tested. The algorithm was then used to produce soil moisture maps of the region for the two study periods.
Abstract
Studies have shown the advantages of low-frequency (<5 GHz) microwave sensors for soil moisture estimation. Although higher frequencies have limited soil moisture retrieval capabilities, there is a vast quantity of systematic global high-frequency microwave data that have been collected for 15 yr by the Special Sensor Microwave Imager (SSM/I). SSM/I soil moisture studies have mostly utilized antecedent precipitation indices as validation, while only a few have employed limited ground observations, which were typically not optimal for this particular type of satellite data. In the Southern Great Plains (SGP) hydrology experiments conducted in 1997 and 1999, ground observations of soil moisture were made over an extended region for developing and validating large-scale mapping techniques. Previous studies have indicated the limitations of both the higher-frequency data and models for soil moisture retrieval. Given these limitations, an alternative retrieval technique that utilizes multipolarization observations was implemented and tested for the SGP region. A technique for extracting algorithm parameters from the observations was developed and tested. The algorithm was then used to produce soil moisture maps of the region for the two study periods.
Abstract
Interfacial evaporation and energy flux are presented for a series of experiments in a laboratory wind wave flume (neutral stratification) with varying free stream velocity and with and without mechanically generated waves. Integral conservation or budget techniques are the means of flux determination. Fluxes normalized to a 6-cm height are independent of fetch, increase with wind speed, and decrease if mechanically generated waves are introduced. Excellent correspondence between normalized energy and mass transfer exists except for the case involving spray which causes a reduction in the thermal field.
Abstract
Interfacial evaporation and energy flux are presented for a series of experiments in a laboratory wind wave flume (neutral stratification) with varying free stream velocity and with and without mechanically generated waves. Integral conservation or budget techniques are the means of flux determination. Fluxes normalized to a 6-cm height are independent of fetch, increase with wind speed, and decrease if mechanically generated waves are introduced. Excellent correspondence between normalized energy and mass transfer exists except for the case involving spray which causes a reduction in the thermal field.
